Hi, interesting, but I think there is not one trustworthy factor to convert Euro spent to CO2 eq (you can buy electricity from coal power, from photovoltaic, or a painting - this will lead to very different "conversion" factors CO2eq/Euro for each product).
Maybe better would be to use exiobase's and ecoinvent's impact method and calculate the GWP for these database. You will need to merge the impact categories for both databases in one method since the two databases are not aligned, but this is probably anyhow good to keep separate. You will thus have a new method with two impact categories, GWP ecoinvent and GWP exiobase (or also more detailed other climate impact categories if you want).
Good luck!
Andreas